Well cementing



WELL CEMENTING Alvin F. Beale, Jr., Louis H. Eilers, and William T. Abel,

Tulsa, O kla assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Application May 23, 1955 Serial No. 510,575

27 Claims. (Cl. 166-29) The invention relates to methods of and compositions for cementing. It'more particularly relates to an improved method of cementing wells drilled into the earth. In boring into the earth for oil, gas, water, or brine, it IS oftentimes necessary, if not desirable, to provide a casing in the bore hole. The casing is usually in the form of a steel pipe. One of the functions of a well casing is to prevent the sides of the bore hole from caving or sloughing into the well. Another function is to provide means to collect the fluids which enter the well hole. The casing also may be used in preventing fiuid from one earth stratum from entering the well while permitting inflow from another. Still other uses of the casing are made depending upon the geology of the earth region involved and the use to which the well is put. In the case of disposal wells, for example, the casing serves to direct the introduced fluid into a particular zone or zones penetrated by the well hole. The casing may extend for the entire length or only a portion of the well here. Communication between the bore of the casing and the adjacent earth may be effected by forming perforations in the casing at appropriate levels.

The successful fulfillment of the functions of a casing in a well hole depends in general upon whether or not the space between the bore hole wall and the outside of the casing can be tightly sealed. Such scaling is necessary to prevent fluid from migrating up or down between the earth and casing. In high pressure wells, it is essential also that the casing be firmly anchored in the hole to keep it in place against the fluid pressure which tends to eject it. Heretofore the almost universal practice of attempting to seal a casing in a well hole has been to deposit in the annular space between the casing and the well hole, in one way or another, a slurry of Portland or gypsum cement and water. The slurry so-deposited is allowed to harden in situ. Although adequate seals are at times obtained, nevertheless numerous difficulties arise in the conventional cementing practice which heretofore have not been adequately overcome. These difliculties militate against achieving the desired objectives of a well cementing operation.

One of these difliculties is that the temperature of the earth formation affects the rate at which the cement slurry stiffens and hardens. In a well hole, it is not always possible to bring about suitable temperature conditions appropriate to the natural setting rate of the cement. As a consequence, severe limitations are oftentimes imposed as to the amount of time available, after the slurry is prepared, during which the slurry remains sufficiently fluid to permit placing it in position in the well as by pumping. In very deep wells, such limitations of time and setting or thickening rates oftentimes make it mandatory to perform the cementing operation in stages. This requires the use of especial equipment and is timeconsuming. In any case after the cement has been manufactured and shipped to the well, its rate of setting cannot be changed much.

EXAMINER Another of the difficulties with conventional well cementing practices results from contamination of .the cement injected into the well. Such contamination is due to the presence in the well hole and in the cracks, crevices, and fissures of the earth formation of material of one kind or another with which the cement slurry comes in contact. These contaminants interfere with the cementing action. Perhaps one of the most disadvantageous of these undesirable materials is the fluid with which the well may be drilled. The drilling fluid is usually present in the well hole during the cementing operation. Both the clay particles, as .well as many of the drilling mud additaments (e. g. quebracho), of which drilling fluids are composed, interfere with the setting of the cement slurries. Clay mud on becoming incorporated in the cement slurry, as it is being placed in position in a conventional casing cementing operation, dilutes and weakens the cement. Clay-base drilling mud also prevents the cement from bonding to the wall of the well hole. Because of the use of mud in drilling the well, the

well wall is coated more or less with a layer of mud or mud cake. In conventional cementing practice, the cement slurry is unable to assimilate the mud in either the fluid or cake form without suffering a loss in strength. In addition, a true seal cannot be produced by the cement in the annular space outside the casing when the earth formation is more or less coated with a mud cake produced in drilling the well hole.

In conventional well cementing practice, especially in wells which are unusually deep, a high hydrostatic pressure is exerted by the cement slurry against the well hole on placing the cement slurry behind a casing. Under these conditions, the difficulty arises that a premature dehydration of the cement slurry may occur. The dehydration results from the filtering action of the earth formation. In this action, the aqueous phase of the slurry is pressed out of it into the earth formation leaving the cement excessively dry. Cement so-dehydrated becomes immobile or unpumpable. For this reason, the dehydrated cement slurry cannot be circulated into position around a casing. The high density of the cement slurry used in conventional cementing operations is a contributing factor to such premature dehydration. Attempts to maintain the cement slurry in a fluid state by agitating the slurry during the stiffening or gelling period also precludes setting with proper strength. Addition of bentonite in attempts to reduce water loss weakens conventional cement.

Some of the cements in common use in conventional well cementing are attacked by saline ground waters, especially those containing sulfate. The destruction of the cement may be brought about prematurely by contact with saline ground water.

Another difliculty in conventional well cementing practice is that the set cement, in an annular space about a casing in a well hole, does not perforate cleanly and without cracking or shattering in the vicinity of the perforation. This is a disadvantage in a well having a casing traversing, for example, a producing oil or gas zone adjacent to a water zone which is to be sealed ofl while obtaining production of oil or gas. In such a situation, perforating the casing opposite the oil or gas zone may result in shatter cracks extending from one level to another in the cemented annulus. Such cracks can admit unwanted water to the well.

Accordingly, it is the principal object of the invention to provide an improved well cementing method which overcomes many of the difliculties inherent in the conventional well cementing operations. Another object is to provide improved cementing material. Still other objects and advantages will appear as the description of the invention proceeds.

' Among the discoveries on which the present invention is based is that a cement comprising phosphoric acid in admixture with an aliiin'iTousfiiai'e'rialYp'reieralaly substahtially alkali free) with which'itis? capable cf reacting, on being placed against the surface of a geological formation, such as the wall of a well hole in the earth, resists filtration, and on being permitted to set in situ becomes bonded thereto even though the surface'm'ay be more or less coated with a clay. Further it has been discovered that by including in the cement comprising phosphoric acid and the aluminous material certain additaments of a more or less water-soluble character new properties are developed which are especially advantageous in forming sealing deposits in the earth, as in cementing a pipe in a well hole. Among the additaments contemplated by the invention are water-sample fluorides, particularly the alkali metal and ammonium fluorides and bifluorides, for example, NH F, NH F.HF, KF, KF.2H O, KRHF, as well as HF or hydrofluoric acid. These aid in determining and controlling the rate at which setting may be brought about. The soluble flu orides improve the tolerance of the cement for contarninating agents, such as drilling muds and drilling mud additaments normally having an adverse action of the setting and cementing characteristics of conventional oil well cements. The soluble fluorides also improve strength and bring about resistance to the softening action o f heat, experienced to a greater or less extent with the cements made with phosphoric acid and the nonsiliceous substantially pure aluminous materials, e. g. gibbsite, but not containing the soluble fluoride additament. Complex more or less water-soluble fluorides also may be used'to accelerate the rate of set, especially at the higher temperatures encountered in the deeper wells currently being drilled, for example, K TiF K SiF KPF (NHQ SiF K CrF KBF HPO F l-l PO F, HPF (NHQ TiR.

are especially advantageous in improving the properties and cementing action in mudded well bores of the cements comprising phosphoric acid and the aluminous material, especially when in the presence of a fluoride. Suitable sourcesv of potassium ion are water-soluble inorganic potassium salts in addition to the potassium compounds listed above, for example, potassium sulfate, potassium phosphate, potassium hydroxide, potassium chromate and pgstassium biEh'riSmate. The corresponding ammonium sa e use'das a source of ammonium ion.

The invention then consists of the improved method of cementing particularly against an earth formation with settable mixtures comprising an aluminous material and phosphoric acid, including improved compositions thereof, herein fully described and particularly pointed out in the claims.

In carrying out the invention, a cement is prepared with one or more suitable aluminous materials, in particulate form, capable of undergoing a cement-forming reaction with phosphoric acid in the presence of water. A wide variety 9f aluminous materials are capable of undergoing the desir'ed ireactionfwith 'phbsplioric lcid, incilidingthe variou's'aluminumoxides, aluminum hydroxides, and aluminum silicates, These materials are generailyw ater-insoluble and contain more than 10 percent by weight of alumina calculated as A1 For reasons of cost and availability, many of the naturally occurring aluminous minerals may be used, as the aluminous material, without purification and with a minimum of processing. Generally milling and drying or calcining suflices to prepare naturally occurring aluminous materials for use. Bauxite, kaolin, and kaolinitic clays are especially suitable. Common clays containing at least percent of A1 0 on the dry basis may be used. The use of an aluminum silicate or aluminum silicate-containing material as the aluminous material has the advantage of rendering the cements resistant to heat-softening at the elevated temperatures encountered in deep wells.

The following Table I sets forth a number of examples of aluminous materials which may be used. They may be ground or otherwise comminuted before use, if necessary. The particle size does not appear to be sharply critical, but is preferably at least as fine as that mostly The presence of the ions of potassium and ammonium passing through a number 40 standard sieve.

Table 1 Analysis, Percent by Weight Aluminous Percent No. Material Ignition Sieve No. Remarks: SOUHA A1 0: SiO; H3O F620: T101 Other 1331. Loss Oxides Gorundum 99 1 1 00 Activated 92 1 7 7 100 7 heated at 1,200 F.

alumina.

57 2 39 1 1 1 40 1 0. 5 micron 65 0 35 35 i 0. 5 micron 65 0 35 35 -100 59 14 23 2 27 40 Pulaski 00., Ark. 53 12 25 3 25 -100 Purified. 5: 13 25 2 24. 5 40 Eufnula, Ala. 55 7 29 3 30 -40 Saline C0,, Ark. 54 i1 28 3 30 -40 Pulaski 60., Ark. 52 2 25 15 -40 D0. 52 1 23 40 Jamaica. 52 16 2-5 4 40 Saline 00., Ark. 50 15 25 6 ---40 D0. 50 14 26 7 -40 Do. 47 24 23 2 40 Pulaski CO., Ark. rio 45 30 21 1 D0.

Knolinitic clay 43 33 19 2 20 -40 Saline 00., Ark. 21. -.do 42 36 19 1 20 40 Pulaski C0., Ark. 22, d0 37 14 2 16 40 D0. 23 Kaolinitic clay, 41 5 5 40 Do.

activated. Kaolinitic clay, 43 53 0 0 -40 #22 heated to 2,400 F.

calcined. Illitlc clay 42 44 10 1 10 40 Texas. Knoitm'te. 39. 5 46. 5 14 14 40 Muscovit 39 45 3 3 325 Anorthite 37 43 0 -40 Grass Valley, Calif.

I I g I v 5 J Table I-Continued Analysis. Percent by Weight Alummpus Percent No. Material Ignition Sieve No. Remarks: Source A110: 810: H3O F810: T10: Other Bal. Loss Oxides Laboradorite 32 50 18 -40 Essex 00., N. Y.

ay- 31 54 11 2 1 5 11 40 Anprtlgosite (pilo- 27 53 1 15 2 -40 Albany 00., Wyo.

e ase Clay- 21 59 i 4 4 11 -40 Texas. Bentonlte 20 60 5 10 2 200 ,Blackhills, So. Dak. Anorthoelasen 19 6B 13 -40 Larvak, Norway. NaK Feidspar..-. 19 67 -40 Nepholinesyenite. 58 1 5 10 11 16 2 -40 Pulaski 60., Ark. Microcline 18 65 0 17 -40 Amelia 00., Va.

18 65 0 17 -40 Kokomo, Col. 16- 63 10 2 2 6 15 -40 Texas. Blotite 10 47 1 15 20 2 2 -40 seplilrilite (vermie- 7 45 20 27 1 -40 Lincoln 00., Mont.

u Fullers earth. 12 60 12 3 12 1 11. 9 -100 Georgia. Bauxiteun 56 11 26 4 3 26 -40 Pulaski 00., Ark.

1 Standard screen scale; minus sign means particles pass through sieve at number indicated.

1 Approximate particle size.

As will be apparent from the examples given in Table I, the aluminous material may contain, as by chemical analysis, not less than about 7 percent of A1 0 The balance of the material may involve silica, in amount not exceeding about 70 percent, Fe O, not exceeding about 20 percent, TiO, not exceeding about 10 percent, and other metal oxides normally comprising aluminous minerals, such as CaO, MgO, K 0, Na,0, in various amounts not exceeding about 30 percent, with or without minor amounts not exceeding about 10 percent of unspecified constituents. \Xzgenmay also bepresentinva; rious amounts depending upon the nature andtreatnrent. if any of the aluminous materiaTand mayarnounttlas much'as about 40 pereentof the weight of the u ndried aluminous material. Excessive amounts of water are not desirable and in some cases the aluminous material may require more or less drying to avoid overloading the cement mixtures with water as will be apparent in what follows.

The aluminous material, phosphoric acid, and an appropriate amount of water as needed, are mixed together in any convenient manner to form aflowabie slurry. The relative amounts of aluminous material and phosphoric acid may be varied over a wide range. The proportions are chosen with reference to the rate at which the slurry is to stiffen and become a monolithic body under the environmental conditions of temperature and pressure that are involved. The temperature, water concentration, and

nature of the aluminous material aflect the rate of set. The mostrapid rates qf setting are obtained with the cafe's or clays prodii'Eeslower setting cements, and the calcined aluminous ,materials, e. g. corundum, and dead burned clays "(2400 F.), the slowest. Unless the environment in which the cemeni is to set is relatively warm as in the deeper wells bauxite is the preferred aluminous material to employ. The particular aluminous material used does not greatly affect the ultimate strength of the cement when the other ingredients of the cement-forming mixture are appropriate.

In general the relative amount of aluminous material and phosphoric acid to produce a cement having the setting time and strength desired can be determined by trial. A trial can be made by mixing batches of the aluminous material with various amounts of phosphoric acid diluted to various concentrations with water and setting aside the resulting mixtures at a temperature at which the cementing operation is to be performed.

As illustrative of this, commercial phosphoric acid (85 percent H P0 balance H O) may be diluted with water, if necessary, and to the resulting solution, while stirring, is added the aluminous material in pulverulent form to make a slurry or cream of fiowable consistency. A number of examples of cement formulation; so made which are pumpable are set forth in Table II using some of the aluminous materials from Table I.

Table II aluminous Water Ratios Material Setting Mix. N0. Lbs. 85% Time at H3130; 175' F No. in Lbs. Lbs. Total Al/P Total Hours Table I Used Added Lbs. HzO/P 6 36. 9 7. 0 56. 1 70 7. 8 63. 6 6 27. 7 14. 1 58. 2 70 2. 9 31. 8 1 18 6 23.1 17. 7 59. 2 70 1. 9 25. 4 1 18 6 18. 5 21. 2 60. 3 70 1. 3 21.1 2 18 6 49. 3 9.4 41. 3 7. 7 40. 9 2 6 37. 0 18. 8 44. 2 60 2. 9 20. 4 5 6 27. 8 26. 0 46. 2 60 1. 6 14. 8 7 6 26. 4 26. 9 46. 7 60 1. 5 14. 8 6 24 6 24. 6 28. 2 47. 2 6O 1. 3 13. 6 5 6 61. 6 11.8 26. 6 50 7. 7 27.0 0. 5 16 6 53. 9 ""17. 7 28. 4 50 4. 5 18. 1 0. 5 16 6 38. 5 29. 4 32. l 50 1. 9 l0. 9 3 6 27. 0 38. 2 34. 8 50 l. 0 8. 4 18 6 23. 1 41. 2 35. 7 50 0. 8 7. 8 24 2 52. 8 47. 2 37. 0 47. 8 2. 3 6. 5 0. 5 16 2 63.0 37. 0 38.3 48.3 3. 6 8.4 0. 5 16 10 104. 0 61. 2 34. 8 2. 1 7. 3 3 18 10 120. O 66. 8 57. 0 97. 1 2. 3 9. 3 4 5 10 80.0 47. l 72. 9 100.0 2.1 13. 6 3 18 10 85. 3 18. 8 95. 8 120. 0 5. 7 40. 8 4 18 21 74. 1 47. 1 78. 8 100.0 1. 5 l3. 6 26 42 21 79. 0 18. 8 102. 2 120. O 4. 0 40. 9 92 22 96. 0 66. 8 57. 0 80. 5 1. 2 7. 7 21 24 31 78. 9 61. 2 60.0 70. 0 0.8 7. 3 31 60. 6 47. 1 92. 3 100. O 0. 8 13. 6 26 42 31 60. 0 9. 9 14. 1 16. 2 3. 7 10. 5 2 24 alumifio usi hydroxides an hydrates, theallirninunfsili- Referring to Table II, the first column lists the mixture number; the second column the number corresponding to that in column 1, Table I, identifying the aluminous material used; the third column the number of pounds of the aluminous material used; the fourth column the number of pounds of 85 percent phosphoric acid used (85 parts by weight H PO 15 parts by weight water); the fifth column the number of pounds of water added (exclusive of that present in the aluminous material, if any, and in the phosphoric acid solution); the sixth column the total number of pounds of water in the mixtures including that in the aluminous material, in the phosphoric, and the additional water of column the seventh column the ratio of the number of moles of aluminum (Al) to the number of moles of phosphorus (P) in the mixtures; the eighth column the ratio of the number of moles of water (H O) of column six to the number of moles of phosphorus (P); and the ninth column lists the setting time in hours.

In Table II, the setting time of the mixtures is the time elapsed after making the mixtures until they acquire an initial set. This initial set is that determined by the apparatus of the vicat setting-time test in accordance with the API recommended practice for testing oil-well cements (API RP B, third edition, April 1953, issued by API Division of Production, 300 Corrigan Tower Building, Dallas 1, Texas). In making the tests for setting time, mixtures to be tested are prepared as described herein and placed in the vicat mold. The mold containing the mixture is maintained at the testing temperature and periodically the mold with the mixure is given the vicat-setting test above mentioned until setting is found to have occurred. Setting occurs over a wide range of ratios of moles of Al per mole of P in the .mixtures which are dilute enough to be flowable yet not so dilute as to fail to set.

In simple pumpable mixtures, i. e. those involving an aluminous material, phosphoric acid, and water without modifying additaments, the ratio of the number of moles of aluminum (Al) to the number of moles of phosphorus (P) in the mixtures may range from about 0.5 to with various amounts of water ranging from about 1.8 to 64 moles of water (H O) per mole of phosphorus (P) in the mixtures. A preferred range of the Al to P ratio in the mixtures is from 0.8 to 3. Within this range of AVF ratios the preferred H O/P ratio ranges from about 5 to 22, where the temperatures encountered by the mixtures are not over about 200 F., and about 1.8 to 10 where the temperatures encountered exceed about 200 F. Similar ratios may prevail in mixtures containing additaments herein mentioned.

Although some separation of liquid from the solids in the cement mixtures may occur as the cement mixtures set, this is an advantage iii environments comprising aluminous materials, such as clays, as in most well bores. The liquid separating from the cementing mixtures when containing free phosphoric acid and particularly soluble fluoride, we have found, is capable of combining with the clays to harden them into a cement-like mass so that the separation of liquid from the cementing mixture assists in obtaining a cementitious bond with the earth formation.

Elevating the temperature of the mixtures of Table II facilitates their setting but softening results on overheating the mixtures in which the alumInGusTfiateriaI'is an oxide,hydrated oxide, or hydroxide, especially when the ratio of H O/P is relatively low. Softening, if any,

of the cement formulations is determined by noting the rate at which one end of a /4 inch round rod sinks into one end of a cylindrical specimen of the set cement. The test may be carried out at various temperatures with a specified loading of the rod. In making a test of this kind, the specimen is held in a cylindrical recess in a metal block, the recess having a size which is just sufiicient to admit the specimen. The temperature of the block and specimen is raised at the rate of 2 to 5 degrees per minute and the rod, loaded to a weight of 150 grams, is suitably supported in a vertical position so as to rest its weight upon the specimen. An additional load of about 2 pounds is applied periodically during the test, in order to break through any crust that may form on the surface of the specimen. Softening, according to this test, is considered to have occurred when the rod, loaded to a total weight of 150 grams, sinks into the specimen below the crust, if any, at the rate of ,4 inch per minute.

After the mixtures acquire an initial set, they are capable of supporting a compressive load and the compressive strength gradually increases with age until full strength is reached. The mixtures will set under petroleum oil, water, or brine encountered in the earth. The rate of hardening under petroleum oil is greater than that under either water or brine. Brines saturated with H S, often encountered in formations penetrated by oil wells, do not adversely affect the rate of hardening of the cement mixtures. The compressive strength of some of the mixtures of Table II, at moderately elevated temperature, are set forth in Table III together with the hours of ageing.

Table 111 Table II Setting Compressive Test No. Mixture Temp., Hours of Strength in No. F. Ageing Lbs. Per

Square Inch Thus by formulating a mixture comprising phosphoric acid and a suitable aluminous material, as exemplified in Table II, and injecting the mixture into the annular space between a casing and the well hole in which the casing is placed, before the mixture acquires an initial set, and then allowing the injected mixture to age in situ the mixture acquires a desirable strength, as indicated in Table III, and seals the casing in place securely to the earth formation.

In some instances, as when it is desired to reduce the cost of the cementing operation, 1 r m be in c g rporated i n the mixtures. The fillers have little or no elftdri the rate of setting but prod uce desirable effecs, other than mere dilution, such as reduction of density when a light filler is used, e. g. coal, and increase in compressive strength when strong an? are used, e. g. sand. Besides sand, and all kinds of powdered coal, powdered glass and like particulated inorganic solid materials, which are not adversely reactive with either the phosphoric acid or the aluminous material, may be used as well as ground nut shells, gilsonite, wood dust, coffee grounds, leather fiber, blast furnace dust, coke, comminuted Bakelite, and the like. In very deep wells, it is oftentimes advantageous to employ a relatively low density filler, such as pulverized bituminous coal, so as to reduce the hydrostatic head created by a long column of the fluid cement formulation which may be present in the well in a cementing operation, thereby reducing fluid and slurry loss. In the following Table IV, examples of cement formulations of the type illustrated in Table II are set forth in which fillers of sand and powdered coal have been added. The resulting mixtures are pumpable and thus capable of being pumped into position in a well hole about a casing therein set.

Table IV Aluminum Wata Filler Ratios Material Setting Mix No. Lbs. 85% Time at H;P04 175 F., No. in Pounds Pounds Total Cool. San AJ/P Total Hours TableI Used Added Pounds Pounds Ponn 1110/? 6 26.4 26.9 46.8 60 one 1.4 14.3 4 5 6 26.4 26.9 46.8 88 1.4 14.3 7 23 6 36. 9 7.0 56.0 70 163. 2 7. 8 63. 6 4% 6 36.9 7.0 56.0 70 11.2 7.8 63.6 4 20 6 18.5 21.2 60.3 70 244. 8 1.3 21. 1 2 18 6 18. 21. 2 60. 3 70 112. 8 1. 3 21. 1 7 23 As previously indicated, overheating the heat-softenable mixture leads to softening or even inhibition of setting. In relatively shallow wells or in wells, the earth formations of which are only moderately hotter than surface temperatures, the simple cement formulations illustrated in Table II suflice to cement the casing. On the amount which may be determined by trial according to the rate of setting desired.

The following Table VI sets forth examples of mixtures containing other fluorides showing the composition, the rate of setting, and the compressive strength after ageing the mixtures. The temperatures are representaother hand, when softening of the cement due to the eletive of those encountered in the earth at various depths.

Table VI Composition of Mixtures Setting Time Compressive Strength Aluminous Soluble Fluoride Water Ratios Mix. No. Material Lbs.

85% HzPOi Lbs. Lbs. Total Age, No. in Lbs. Kind Lbs. Added Total All? HzO/P F/P F. Hrs. Hrs. F. P. s i Table I Used 1 250 118 KF .2T'Ir0.-- 50 82. 1 119. 1 4. 8 6. 5 0. 52 175 28 72 250 2, S00 4 28. 7 AIFLHSO..- 10 0 13. 0 1. 0 2. 9 1.18 175 1 72 175 5.000 4 20 25. 3 NaaAlFa. 10 0 10. 8 1. 2 2. 7 1. 3 175 0. 5 18 175 4, 400 9 11. 8 2. 25 8. 2 18. 7 3. 9 10. 2 0. 77 75 2 76 72 4, 000 4 64 15.1 0 HF... 11 9. 9 40.1 6. 3 16. 0 2.1 75 3 72 76 2, 500

vated temperature of the environment cannot be tolerated, we have found, softening can be controlled by including in the cement mixtures a soluble fluoride. The addition of soluble fluoride has the advantage also of increasing the strength and bringing about setting at temperatures at which, in the absence of soluble fluoride, the mixtures exhibit undesirably long setting times. The presence of soluble fluoride can be used to modify the rate of setting to suit the case in hand and thus increases the range of usefulness of cement formulations comprising the aluminous material and phosphoric acid.

In the mixtures, as for example those of Table VI, the fluorine content, derived from the fluoride, may vary over a wide range in relation to the phosphorus content which is derived from the phosphoric acid. This rela-- tion is expressed by the F/P ratio, as already indicated. This ratio may range, for example, from 0, when no fluoride is added, up to about 10 depending upon the rate of setting desired at the temperature at which the mixtures are to set and age-harden. A preferred range is from 0.025 to 2.0 for the ratio F/P.

Small amounts of soluble fluoride suflice to overcome In Table V mix numbers 33 and 34 are examples showing the effect of a soluble fluoride in shortening the setting time of mixes 15 and 18, respectively, of Table II. By the addition of a soluble fluoride setting of the phosphoric acid-aluminous material-water mixtures is brought about more rapidly and at a lower temperature. By varying the ratio of the number of moles of fluorine (F) per mole of phosphorus (P) in the mixtures different rates of setting may be obtained. In the examples given in Table V, the ratio of the numbers of moles of fluorine to the number of moles of phosphorus in the mixes is given as 0.52 in the column headed F/P. Other waterthe heat softening characteristic of the mixtures made with those aluminous materials which yield heat-softenable mixtures. For example, from about 0.4 to 3 percent fluorine, derived from a water-soluble fluoride, suffices to control heat softening.

Similar results are obtainable by using a relatively insoluble fluoride, such as aluminum fluoride or calcium fluoride (CaF together with a more or less stoichiometrical equivalent amount of an acid, such as sulfuric acid, or other soluble sulfate, such as K 50 or Al,(SO capable of decomposing the fluoride to liberate in the mixture the soluble fluoride constitutent. Ex-

soluble inorganic fluorides may be used similarly in an amples of mixtures employing a fluoride, e. g. CaF decomposable by a soluble sulfate are set forth in Table In obtaining a measure of the strength of the bond, VII. The formulatlons may contain 2 percent or less to securing the cements to the surface of an earth formation, as muchas 20 percent by weight of such fluoride. tests were made with the mixes of Table VIII. In the Table VII Composition of Mixtures Setting Time Alumlnous Fluoride Sulfate Water Ratios Mix. No. Material Lbs. 35% H1P04 Lbs. Lbs. Total No.in Lbs. Kind Lbs. Kind Lbs. Added Total All? H1011 F/P F. Hours Table I Used 22 2,400 1,671 Cal": 750 H1504 342 1,450 2,010 1.2 7.7 1.32 175 72 12 41.3 24.1 F, 34 K2804 6.3 346 40.3 2.1 13.2 1.03 30 2 17 21 42.0 31.2 cam 3.0 AI1(SO4)16%H1O 3.0 26.3 30.4 1.3 3.0 0.23 175 2 1 Mix contains 6 pounds of A5101 as a corrosion inhibitor and 45 pounds of the sodium salt of a condensed naphthalene sull'onlc acid as a dispersant.

In preparing the cementing mixtures containing 3. tests cores of natural sandstone were used to simulate an soluble fluoride or having soluble fluoride-yielding mateearth formation. The cores hadapermeability of approxirial therein, the aluminous material may be mixed with mately 2 millidarcys. The cores were cylindrical in form the phosphoric acid solution suitably diluted, if at all, with 3.5 inches in diameter and 10 inches long. For the tests water first and then the fluoride constituent may be added. the cores were prepared as follows. A hole 1.25 inches in If the fluoride constituent is water-soluble, it may be put diameter was bored into one end to a depth of 8 inches into solution in water or in the requisite amount of diluted 5 along the longitudinal axis. The wall of the hole was phosphoric acid and the solution then mixed with the coated with a mud cake formed by forcing into the hole an aluminous material. In making such mixtures, it is apaqueous drilling mud. By weight, the mud was comparent that some of the water may be added as a conposed of bentonite 4.4 percent, crude sodium tannate 1.0 stituent of the phosphoric acid, some as a constituent of percent, sodium hydroxide 2.0 percent, the balance being the soluble fluoride solution, if such be used, some as a water. The mud had the following properties: constituent of the aluminous material, if not anhydrous, and the balance of the water, if any, as liquid water.

However the water is present in or added to the mixtures Marsh funnel viscosity 41 seconds. so-made, due account must be taken of the total amount of Fluid 108s 9 ml. per 30 mm. water so that desirable H O/ P ratios are not exceeded. Denslty 8.7 lbs./ gal.

It is a feature of the invention that by setting the cements against the earth formation, as in a mudded well bore, bonding to the earth by the set cement takes place. while fOTemE h 8 8 mudtlnto h e the q h This enables a true seal to be obtained between the casing was supported e P P PP 4 lhche$ ll1 diameter W1th of a well and the earth formation in which it is cemented. the P between the core and the Inside of the pp The presence of fluoride in the cement formulation, espefilled with e A Pressure of 100 P- maintained cially wh n th fl id i dd d as a pgtassium or on the mud in the core for one hour. Bentomte was theremonium fluorine salt, enhances the bonding. Advani filtered from the mud y the core forming a cake uI901! tageous results as regards bonding are obtained by the inthe Wall Of the hole- The liquid Portion of the mud thus clusion of suflicient fluoride in the mixtures to produce 5 filtered out seeped into or through the core into the sand therein, in general, a fluorine-phosphorus ratio, F/P, of around it. After forming the mud cake, the fluid mud 0.02 to 10. Preferred ratios of F/P are about 0.1 to 2. remaining in the hole was displaced with the cement The following Table VIII sets forth examples of cement formulation to be tested using a freshly prepared core formulations and the strength of the bond obtained in for each test. The cement formulation thereby filled the accordance with the test described below. mudded hole in the core. The cement formulation was Table VIII Composition of Mixtures Bonding Strength Aluminous Fluoride Sulfate Water Ratios Material Mix Lbs. No. Lbs. Lbs. Dis- No. A240; pers- Total F. Hrs. P.s.i.

in Lbs. H1P01 ant 1 Lbs. Lbs. Table Used Kind Lbs. Kind Lbs. Added Total All? H o 21 2,400 1,671 12 45 1,424 2,104 1.35 3.1 175 72 15 21 2,400 1,671 car, 750 12 45 1,424 2,104 136 3.1 1.33 175 72 162 22 2,400 1,671 081, 750 K460. 600 6 45 1,424 1,034 1.2 7.3 1.33 175 72 30 22 2,400 1,671 K2801 600 6 45 1,424 1,984 1.2 7.6 22 2,400 1,671 REP, 30 6 45 1,424 1,034 1.2 7.6 0053 175 72 22 2,400 1,671 XHF, 300 6 46 1,424 1,034 1.2 7.6 0.53 72 103 22 2,400 1,671 08F: 750 H4801 342 6 45 ,450 2,010 1.2 7.7 1.33 175 72 103 22 1,005 751 9g}, K1804 300 6 45 1,136 1,464 2.2 12.5 2.12 175 72 70 4 1,005 751h3 K1804 300 6 30 1,136 1,003 30 17.0 2.12 175 72 31 22 060 751{ ;3 g b 53} 6 13 1,136 1,320 107 11.2 1.3 175 72 163 I Polymerized sodium salts of alkyl naphthalene sulionic acid. 1 Contains 1,200 lbs. of powdered bituminous coal as a filler. 8 Greater than specimen which broke in test.

13 then pressed against the mudded wall of the hole by applying a pressure of 200 p. s. i. to the formulation in the core. During the application of this pressure, the core was maintained at 175 F. for 48 hours while the cement was thereby hardened in situ.

After the cement formulations had set, the cores soprepared were cut into short lengths. This was accomplished by sawing each core in a plane perpendicular to the axis. The length of the sections so-obtained was from 1 to 4 inches. The sections so-obtained comprised an annular ring of core with a solid cylindrical plug of cement bonded to the inside through the mud cake. The bonding strength was measured by ascertaining the force required to break the bond between the cement and the inside of the core section on pushing out the solid plug of cement. The force in pounds thus measured divided by the area in square inches of the inside of the section of core is the figure recorded in Table VIII as the bonding strength in p. s. i.

Similar tests were made with Portland cement for comparison. In these tests the Portland cement solidified in the mudded hole of the core in each instance as a more or less cylindrical chunk separate from and unbonded to the wall of the hole. The chunk of Portland cement fell out of each core on being sectioned. There was no evidence of bonding.

Referring to Table VIII, showing bonding strength measurements, mix 43 is an example of a cement formulation using an aluminous material and phosphoric acid, without additaments other than a corrosion inhibitor A 0, and a dispersant. The bonding strength is that obtained in the test above described after allowing the mix to set for 72 hours. The bonding strength of the formulation of the kind illustrated by mix number 43 is improved by the addition to the mix of CaF; as exemplified by mix number 44 using the same aluminous material as mix number 43. Mix number 45 is illustrative of the bond strength of a similar mix to that of number 44 but using a different aluminous material and containing K 50 With this aluminous material (#22) potassium sulfate in the formulation is illustrated in mix number 46. A much smaller proportion of KHF, in place of CaF, or K 50 improves the bond as exemplified by mix number 47. In mix 47 the ratio of F/P is 0.053; larger amounts of KHF as in mix 48, in which the ratio F/P is 0.53, produce about the same strength of bond. The combined use of calcium fluoride and sulfuric acid as in mix number 49 produces substantially.

the bonding strength obtainable with KHF, as the sole source of fluorine but with the advantage of lower cost. Mixes having a high bonding strength and other desirable characteristics may contain three additaments, exclusive of the corrosion inhibitor and the dispersant, e. g. CaF KHF and K 80 Examples are mix numbers 50 and 51 using different aluminous materials. Improved bonding results on including in the mixes the combination of the sulfates of ammonium and potassium along with CaF, and KHF An example of such a mix is number 52. Either the corrosion inhibitor or the dispersant or both may be omitted without substantially affecting the bonding action.

The presence of potassium salts, such as potassium sulfate and potassium phosphate or ammonium salts, such as ammonium sulfate and ammonium hydrogen phosphate, for example, in concentrations of about 1 to 15 percent by weight, like soluble fluoride, enables the cement formulation of the aluminous material and phosphoric acid to resist heat softening up to a temperature of at least 500 F. Such cement formulations are especially advantageous in cementing casing in very deep wells the earth formation of which is excessively hot. The following four mixes, 53 to 56 inclusive, are examples of a cement of this kind. The mixes are made by mixing together the listed ingredients.

Mix No. 53: Pounds Aluminous material #10 of Table I Phosphoric acid (85%) 66.9 Water 56.9 Potassium sulfate 24.0

At F. the mixture sets in less than 10 hours. At 78 F. it sets in about 71 hours. On being aged at 130 F. 144 hours after setting, the aged mixture may be heated to 500 F. without softening.

Mix No. 54: Pounds Aluminous material #4 of Table I 45 Phosplrdfic acid (85%) 45 AmmonTu'fn hydrogen phosphate 10 On mixing the foregoing ingredients at 212 F. in the order listed, the mixture resists softening on heating to 500 F. after ageing for 72 hours at 78 F.

Mix No. 55: Pounds Aluminous material #4 of Table I 33 Phosphoric acid (85%) 60 Potassium phosphate (K PO 7 0n mixing the foregoing ingredients at 212 F. in the order listed, the mixture resists softening on heating to 500 F. after ageing for 72 hours at 78 F.

Mix No. 56: Pounds Aluminous material #4 of Table I 39 Phosphoric acid (85%) 46 Potassium bifluoride (KRHF) 15 On mixing the foregoing ingredients at 78 F. in the order listed, the mixture resists softening on heating to 500 F. after ageing at 78 F. for 72 hours.

Although mix numbers 54 and 55 were prepared at 212 F. lower temperatures may be employed such as those ordinarily prevailing at the earth's surface.

In addition to the advantageous effects on preventing heat-softening already mentioned, the ions of K and NE; in the cement formulations give rise to improved properties particularly as regards compressive strength and especially when used in formulations containing also a soluble fluoride. The amount of potassium or ammonium employed may produce a ratio of K or (NH to P in the mixtures of up to 3. A generally useful range for the ratio is between 0.2 and 2.0.

As already indicated, certain additaments added to the cement formulation in particular combinations are especially advantageous. Among such combinations of additaments contemplated by the invention are potassium sulfate and potassium bifluoride; potassium sulfate and ammonium bifluoride; calcium fluoride and potassium sulfate; calcium fluoride, potassium sulfate and ammonium bifluoride; potassium bifluoride and potassium phosphate; potassium bifluoride and ammonium phosphate. Some examples of the combined use of such additaments appear in previous tables.

By using various amounts of potassium bifluoride in combination with potassium sulfate in cement formulations comprising the aluminous material, phosphoric acid, and calcium fluoride, with or without the inclusion of a filler, a wide range of setting times together with bonding to the earth and high strength may be had at the temperatures encountered in deep wells.

The slurries of the cements herein comprising a clay exhibit a gel strength of from about 200 to 600 grams measured in accordance with the standard procedure used in testing drilling muds. As made, such slurries immediately gel more or less but upon agitation the gel strength decreases. It is desirable to include in such slurries, in order to reduce their gel strength, a waterand acid-soluble anionic dispersing agent, such as an alkyl aryl sulfonate or alkali metal salt thereof. Some of the formulations already exemplified contain a dispersant as indicated. The amount which may be added is not critical since the effect on the gel strength is more or less proportional to the amount used up to about 3 percent by weight of the slurry. Lesser amounts produce a lesser effect on gel strength reduction. For example, a slurry composed of 43.7 pounds of kaolinitic clay (No. 21 of Table I), 37.6 pounds of 85 percent phosphoric acid, 14.9 pounds of calcium fluoride, 11.2 pounds of K 50 1.8 pounds of KHF 53.6 pounds of water, and 59.7 pounds of pulven'zed bituminous coal, as a filler, has an initial gel strength of 275 grams; after 10 minutes of standing the gel strength increases to 300 grams. On adding to the slurry 0.4 percent of the sodium sale of naphthalene sulfonic acid condensed with formaldehyde (Tamol N), the initial gel strength is only 35 grams and on standing for 10 minutes the gel strength increases only to 50 grams. Other examples of suitable dispersing agents are the polymerized sodium salts of alkyl naphthalene sulfonic acid (Daxad 11); the sodium salt of polymerized alkyl aryl sulfonic acid condensed with formaldehyde (Darvan 1); the high molecular weight alkyl aryl sodium sulfonates (Naccotan A). The dispersing agents which are used to decrease the gel strength do not adversely affect the cementing action of the slurries.

In cementing wells using the more complex formulations, it is advantageous to mix together first the alumi- 'nous material, phosphoric acid (more or less diluted with water) and filler if used. If calcium fluoride is to be included in the formulation, it may be added along with the aluminous material. The mixture so-prepared sets more or less slowly largely depending upon the temperature and activity of the aluminous material which may be chosen for the formulation so that plenty of time is available in which to incorporate the other additaments. At about the time the well is to be cemented, the other additaments of the formulation may be added as desired and mixed in thoroughly. These other additaments may comprise soluble fluoride which speeds up the setting time and potassium sulfate which promotes greater strength. Ammonium sulfate may be added also if desired. At this stage, a dispersant may be added to the mixture so as to reduce the gel strength and thereby facilitate pumping. The mixture is then ready for injection into the well in the usual way to cement the casing.

The amount of filler the mixtures can tolerate varies over a wide range and depends to some extent upon the bulkiness of the aluminous material used and the degree of fluidity it is desired the mixtures should have. In

general the amount of filler will'not exceed about 200 percent of the weight of the aluminous material. For example a generally useful amount to use with a bauxite as the aluminous material is a weight of about 125% of that of the bauxite. With a kaolin as the aluminous material, the filler may amount to as much as 150 percent of the weight of the kaolin.

The following mixes of general utility and preferred composition are examples of cement formulations designed for use over three ranges of temperature most commonly encountered in the well. These mixes are most advantageously prepared by mixing together in powder form certain of the dry ingredients, viz. the aluminuous material, filler, calcium fluoride, potassium sulfate, and dry powdered dispersant, if used, so as to form a dry mix. The dry mix may be put up in sacks or other convenient form of package suitable for storage or transportation.

The dry mix may be transported to the site of the cementing operation and there mixed with phosphoric acid and water to form a fluid self-hardening slurry. The addition of soluble fluoride (e. g. KHF which speeds up the setting rate, is incorporated in the mixture as desired following the addition of the phosphoric acid and water. The mixture so-prepared is then ready for use in the cementing operation and will set within a time predetermined by the kinds and proportions of the ingredients. At the temperature for which the mixture is designed, other things being equal, the lapse of time before setting occurs depends upon the amount of soluble fluoride added. Examples of three dry formulations, mix A, B, and C, are set forth in the following Table IX.

l Polymerized sodium salts of alkyl naphthalene sulfonic acid.

Referring to Table IX, it will be observed that each dry mixture is compounded of a different aluminous material. Mixes A and C employ aluminous materials 10 and 22, respectively, and mix B employs a mixture of 10 and 22. Each dry mix is designed to provide a cement for use over a different range of temperature. The ranges overlap somewhat and cover most of the temperatures encountered in well cementing operations. Such dry formulations, and in particular those of Table IX, may be mixed with diluted phosphoric acid (phosphoric acid and water) using an appropriate amount thereof to form a cementing slurry as shown in Table X.

Table X Lbs. of Water and HaPOi g/ofiAdd Per Lbs. of Dry Dry Mix Dry Mix Dry Mix A B C H2O 27. 6 25. 6 26. 2 85% HsPOt 23. l 27. 7 28. 1

Table XI Mix A Mix B Mix Temperature 01 Setting F. Kim, Lbs. For 100 Lbs. of Dry Mix Hours 0! Setting Time Although the invention has been described more particularly with reference to forming a monolithic body as a seal between the wall of a well hole in the earth and a well casing therein, it will be apparent that sealing deposits can also be formed in an uncased portion of a well hole as for example in the hole below a casing, or other hole in the earth, where the cement formulation may be brought into contact with and set against an earth surface.

Among the advantages of the invention are that the rate at which sealing or setting of the cement in situ may be brought about is subject to a wide range of control; the method is usable over the wide range of temperatures encountered in the earth formations pene: trated by wells to be cemented; the cement formulation on being deposited in a well hole resist loss, by filtration, of its liquid portion and thus remains pumpable i under adverse well condinons in which other cements suffer a damaging liquid loss; drilling mud and drilling] mud additamentsare tolerated by the iefiihtfima tionsto--ari" extentwhich does not prevent obtaining "a proper seal between the well hole and the well casin therein; the cementing method produces a true bond with the mudded wall of the well hole in an eart formation; fillers may be included in the formulation for lowering the cost, and for reducing or increasing th density as desired; the cement formulations are easil and rapidly prepared and injected without difliculty pumping into the well.

We claim:

1. The method of cementing a well formed in the earth which comprises depositing therein into contact with the earth formation a flowable self-hardening mixture consisting of an aluminous material in particulate form selected from the group consisting of the oxides, hydroxides, and silicates of aluminum, phosphoric acid, and water, the ratio of the number of moles of aluminum (Al) to the number of moles of phosphorus (P) in the mixture being between 0.5 and 20, and the ratio of the number of moles of water (H O) to the number of moles of phosphorus (P) in the mixture being between 1.8 and 64.

2. The method according to claim 1 in which there is incorporated in the mixture a filler of a particulated solid unreactive with the phosphoric acid and the aluminous material.

3. The method according to claim 1 in which the mixture includes an inorganic fluorine compound.

4. The method according to claim 1 in which the mixture includes a water-soluble inorganic fluoride selected from the group consisting of ammonium fluoride, ammonium bifluoride, potassium fluoride, potassium bifluoride, and hydrogen fluoride.

5. The method according to claim 1 in which the mixture includes a water-soluble inorganic sulfate and calcium fluoride.

6. The method according to claim 1 in which the mixture includes calcium fluoride and a water-soluble sulfate selected from the group consisting of K 80 H 80 and (NI-10 80 and a water-soluble fluoride selected from the group consisting of ammonium fluoride, ammonium bifluoride, potassium fluoride, potassium bifluoride, and hydrogen fluoride.

7. The method according to claim 1 in which the mixture includes calcium fluoride, potassium sulfate, and potassium fluoride, and the ratio of F/P is between 0.02 and 10.

8. The method according to claim 3 in which the ratio of the number of moles of fluorine (F) derived from the fluorine compound to the number of moles of phosphorus (P) derived from the phosphoric acid is between 0.02 and 10.

9. The method according to claim 3 in which the fluorine compound is selected from the group consisting of the fluophosphoric acids, potassium fluotitanate, ammonium fluotitanate, ammonium fluosilicate, potassium fluosilicate, potassium borofluoride, potassium fluochromite.

10. The method according to claim 7 in which the ratio of K/P is between 0.2 and 3 and the mixture includes ammonium sulfate.

11. The method according to claim 1 in which the mixture includes aluminum fluoride, and a water-soluble sulfate selected from the group consisting of K 50 H 80 and (NH SO and a water-soluble fluoride selected from the group consisting of ammonium fluoride, ammonium bifluoride, potassium fluoride, potassium bifluoride, and hydrogen fluoride.

12. The method according to claim 1 in which the mixture includes calcium fluoride, potassium sulfate, and potassium bifluoride, and the ratio of F P is between 0.02 and 10.

13. The method of forming a fluid mixture capable of hardening into a monolithic body which consists in mixing together an aluminous material in particulate form selected from the group consisting of the oxides, hydroxide and silicates of aluminum, phosphoric acid, and water so as to produce a fluid slurry in which the ratio of A1 to P is between 0.5 and 20 and the ratio of H 0 to P is between 1.8 and 64, and incorporating in the slurry an inorganic fluorine compound selected from the group consisting of ammonium fluoride, ammonium bifluoride, potassium fluoride, potassium bifluoride, and hydrogen fluoride in amount suflicient to provide therein a ratio of F to P of from 0.02 to 10.

14. The method according to claim 13 in which there is included in the slurry a water-soluble inorganic sulfate and calcium fluoride.

15. The method according to claim 14 in which the water-soluble inorganic sulfate is potassium sulfate in amount suflicient to produce therein a ratio of K/P of up to 4.

16. The method according to claim 14 in which the water-soluble inorganic sulfate is ammonium sulfate and is present in amount sufficient to produce therein a ratio of NH /P of up to 4.

17. The method according to claim 13 in which the fluorine compound is selected from the group consisting of the fluophosphoric acids, potassium fluotitanate, ammonium fluotitanate, ammonium fluosilicate, potassium 19 fluosilicate, potassium borofluoride, potassium fluochromite.

18. A self-hardening mixture consisting of a waterinsoluble naturally occurring aluminoug gatgrial in particulate form containing at least" percenfofAbO by weight, hos horic acid in amount suflicient to provide in the mixture a raflo of AV? of between 0.5 and 20, a L,- selected from the group consisting of uoride, potassium bifluoride, the fluophospotassium "hydrogen fluoride, potassium fiuotitanate ammonium fluotitanate, ammoniurr fluosmcate otassium flu cate potassiumbdr'dfluoride, potassium fluochrgmitejn unt su cient to provide a ratio of F/P of between 0.02 and 10, and r including that, if any, occurring with the aluminous ftfiat'erial, phosphoric acid and the fluoride, in amount sutficient to provide a ratio of H O/P of between 1.8 and 64.

19. A self-hardening mixture according to claim 18 including a water-soluble My in amount between 1 and percent by weight, and in amount between 2 and percent by weight of mixture.

20. A self-hardening mixture according to claim 18 including a soluble sulfate selected from the group consisting of amm lfate and pgtagsjum ulfate in amount between'T'and 15 perc'em dcalcium fluoride in amount between 2 and 20 percent by WOIEEI of The inixture.

21. The method according to claim 13 in which there is included in the slurry a water-soluble inorganic sulfate selected from the group consisting of K 50 H SO and (NH SO and aluminum fluoride.

22. A self-hardening mixture according to claim 18 including a water-soluble inorganic sulfate in amount between 1 and 15 percent by weight, and aluminum fluoride in amount between 2 and 20 percent by weight of the mixture.

23.'A self-hardening mixture according to claim 18 including a soluble sulfate selected from the group consisting of ammonium sulfate and potassium sulfate in amount between 1 and 15 percent by weight, and aluminum fluoride in amount between 2 and 20 percent by weight of the mixture.

24. The method according to claim 1 in which the aluminous material is clay.

25. A dry formulation capable of forming a selfhardening mixture on being mixed with phosphoric acid and water to form a flowable slurry consisting of a mixture of 10.2 to 11.2 parts by weight of calcium fluoride; from 35.6 to 41 parts of bauxite; and from 7.2 to 7.8 parts of potassium sulfatef 26. A dry formulation capable of forming a self-hardening mixture on being mixed with phosphoric acid and water to form a flowable slurry consisting of a mixture of 10.2 to 11.2 parts by weight of calcium fluoride; from 35.6 to 41 parts of kaolinitic cl ay; and from 7.2 to 7.8 parts of potassium stfifate.

27. A dry formulation capable of forming a self-hardening mixture on being mixed with phosphoric acid and water to form a flowable slurry consisting of a mixture of 10.2 to 11.2 parts by weight of calcium fluoride; from 35.6 to 41 parts of vermiculite; and from 7.2 to 7.8 parts of potassium sulfate.

/ References Cited in the file of this patent UNITED STATES PATENTS 225,817 Fletcher Mar. 23, 1880 1,507,379 Hoskins Sept. 2, 1924 1,556,115 Hoskins Oct. 6, 1925 1,908,636 Langenberg et al. May 9, 1933 2,146,480 Kennedy Feb. 7, 1939 2,188,767 Cannon Jan. 30, 1940 2,218,058 Stalhane Oct. 15, 1940 2,285,302 Patterson June 2, 1942 2,391,493 Wainer Dec. 25, 1945 2,450,952 Greger Oct. 12, 1948 2,562,148 Lea July 24, 1951 FOREIGN PATENTS 20,302 Great Britain of 1907 440,302 Great Britain Dec. 24, 1935 

1. THE METHOD OF CEMENTING A WELL FORMED IN THE EARTH WHICH COMPRISES DEPOSITING THEREIN INTO CONTACT WITH THE EARTH FORMATION A FLOWABLE SELF-HARDENING MIXTURE CONSISTING OF AN ALUMINOUS MATERIAL IN PARTICULATE FORM SELECTED FROM THE GROUP CONSISTING OF THE OXIDES, HYDROXIDES, AND SILICATES OF ALUMINUM, PHOSPHORIC ACID, AND WATER, THE RATIO OF THE NUMBER OF MOLES OF ALUMINUM (AL) TO THE NUMBER OF MOLES OF PHOSPHORUS (P) IN THE MIXTURE BEING BETWEEN 0.5 AND 20, AND THE RATIO OF THE NUMBER OF MOLES OF WATER (H2O) TO THE NUMBER OF MOLES OF PHOSPHORUS (P) IN THE MIXTURE BEING BETWEEN 1.8 AND
 64. 